The limited mechanical properties of Al and its alloys adversely affect its applications in automobile and aerospace industries. This remains one of the major concern in the fabrication to suit its application in recent days. The main aim of the present work is to improve the fracture toughness of the Al matrix composite . A composite with Al 6061 alloy as matrix and Zirconium Oxide as reinforcement is fabricated by stir casting process. The specimens were prepared according to ASTM standards and fracture toughness, tensile and hardness tests were performed and the properties were investigated. Zirconium oxide is selected as a reinforcement because of its ability to influence the microstructure of the Al 6061 alloy to improve the fracture toughness. The fracture toughness is highest at 6% reinforcement of ZrO2 and hardness is found to be more at 4% reinforcement

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Studies On Fracture Toughness Behavior of Hybrid Aluminum
Metal Matrix Composites
Arun C Dixit U1
, Mamatha.Y.P2
, Balu Vijay S N3
, Shivashankar R4
1,2,3,4
Department Of Mechanical Engineering, Vidyavardhaka College Of Engineering, Mysuru -02
ABSTRACT
The limited mechanical properties of Al and its alloys adversely affect its applications in automobile and
aerospace industries. This remains one of the major concern in the fabrication to suit its application in recent
days. The main aim of the present work is to improve the fracture toughness of the Al matrix composite . A
composite with Al 6061 alloy as matrix and Zirconium Oxide as reinforcement is fabricated by stir casting
process. The specimens were prepared according to ASTM standards and fracture toughness, tensile and
hardness tests were performed and the properties were investigated. Zirconium oxide is selected as a
reinforcement because of its ability to influence the microstructure of the Al 6061 alloy to improve the fracture
toughness. The fracture toughness is highest at 6% reinforcement of ZrO2 and hardness is found to be more at
4% reinforcement.
Keywords: Fracture Toughness, Zirconium Oxide, Al 6061, SENB, Stir Casting, Metal Matrix Composite.
I. INTRODUCTION
Aerospace applications are the original
driving force for metal matrix composite
development. This is due to the quest for weight
reduction for improved performance and payload
capabilities combined with high value placed on
weight savings. In the automotive market, properties
of interest to the automotive engineer include
increased stiffness, wear resistance, improved cycle
fatigue resistance and fracture toughness. Weight
saving is also important in automotive applications
for achieving performance. In commercial and
industrial sector, improved performance is highly
valued. As a result, many materials that gain favour
in aerospace and automotive industries are also
applied in this sector. Metal matrix composites gives
the solution to the contemporary problems,
considering the factors like cost effectiveness and
hostile environmental conditions.
II. METHODOLOGY
The main objective of this work is to
fabricate Al6061-ZrO2 metal matrix composite by stir
casting process, to prepare specimens and investigate
tensile, hardness and fracture toughness properties
according to ASTM standards. Finally analysing the
microstructure of the composite.
III. MATERIAL SELECTION
Matrix Material- Al 6061
Table 1 Composition of Al6061 alloy
Manganese 0.15%
Iron 0.70%
Copper 0.15-0.40%
Magnesium 0.15%
Silicon 0.4-0.8%
Zinc 0.25%
Chromium 0.4-0.35%
Aluminium 0.05-0.15%
Others 95.8-98.6%
Table 2 Composition of Al 6061 & ZrO2 for
specimen preparation
S.No Reinforcement %
Specimen 1 As Cast Al 6061
Specimen 2 2%
Specimen 3 4%
Specimen 4 6%
Specimen 5 8%
Specimen 6 10%
Fabrication By Stir Casting
The quantities of zirconium oxide were
taken in a crucible and was heated to a temperature of
400o
C for 15 mins. Al 6061 was heated in the
furnace at a temperature of 900o
C.The molten
material was stirred with a stirrer speed of 220 rpm to
create vortex , then the heated reinforcements were
added and stirred. The composites were cast using
conventional methods.
Fig 2 Stir Casting Apparatus
RESEARCH ARTICLE OPEN ACCESS

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ISSN : 2248-9622, Vol. 6, Issue 7, ( Part -1) July 2016, pp.43-46
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Specimens for Investigation
Fig 3 Fracture Test Specimens
Fig 4 Tensile Test Specimens
Fig 5 Hardness Test Specimens
Fig 3, 4, 5 shows the specimens prepared for fracture,
tensile and hardness test according to ASTM E 1820-
13, E 8, E 10.
IV. TESTING FRACTURE TEST
The Fracture toughness is determined as per
ASTM-E1820-13. The specimens were tested with a
span length of 65mm using three point bending with
10 ton capacity of computer controlled UTM. The
rate of loading was kept at 1mm/min. The total span
of the specimens was 65 mm. The single edge notch
bend (SENB) specimens were used to determine the
fracture toughness.[2] The experimental setup is as
shown in fig.6.
Fig. 6 Three Point Bending Fracture Test Method
Tensile Test
Tensile Test was carried out on a
computerized UTM according to ASTM E8.The
experimental setup is as shown in figure 8.
Fig.7 Tensile Test Specimen
Fig 8 Universal Testing Machine to perform Tensile
Tests.
Hardness Test
Hardness test was done with standard Brinell
Hardness Testing Machine. Test was perfomed
according to ASTM E10.
Fig 9 Brinell Hardness Testing Machine
Microstructure Study and Analysis
Microstructure is the microscopic definition
of each constituents in the material. Precisely, it’s the
study of crystalline structure , composition, size,
interaction, orientation and eventually their effect on
macroscopic behavior in terms of toughness,
hardness, tensile and compressive strength and
corrosive resistance

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V. RESULTS AND DISCUSSION
Tensile Test Results
Table 3 Tensile and Yield Strength for various
wt.% of reinforcenment
Specimen Tensile
Strength in
N/mm2
Yield Strength
N/mm2
As cast Al
6061
147.65 134.61
2% 124.058 108.376
4% 126.772 113.896
6% 104.233 92.934
8% 96.686 87.975
10% 96.775 89.228
0
20
40
60
80
100
120
140
160
AsCast
2%
4%
6%
8%
10%
Tensile
Strength
Yield
Strength
Stress in
N/mm2
Fig 10 Variation of Tensile and Yield Strength for
different composition of ZrO2
It can be seen that there is a decrease in
both tensile and yield strength of the composite as
the weight fraction of the reinforcement is
increased. This decrease is more pronounced at the
Al6061+6%ZrO2 composition. When Zirconia is
under tensile or compressive strain by external
force, its structure will be changing from tetragonal
phase to mono-clinic phase, and it is similar with
“Martensitic transformation” which is caused by
steel quenching. The unique phenomenon which is
utilizing phase transformation to absorb energy and
increase ceramic toughness, is called “Stress-
induced phase transformation”. Also the decrease
in molecular spacing, because of increased weight
of ZrO2 causes resistance to dislocations. Thus, we
can witness the reduction in the tensile properties
of the composite.
VI. FRACTURE TEST RESULTS
Table 4 Fracture Toughness for various wt.% of
reinforcenment
Specimens Fracture
Toughness
Mpa√m
As cast Al
6061
25.64
2% 21.37
4% 22.79
6% 31.01
8% 18.521
10% 18.28
Composition of Al-ZrO2 Composite
0
5
10
15
20
25
30
35
AsCast
2%
4%
6%
8%
10%
Fracture
Toughness…
Fig 11 Variation of Fracture Toughness for
different composition of ZrO2
From the graph, it can be seen that the fracture
toughness decreases with 2% ZrO2 and reaches the
peak value at 6% ZrO2 and the fracture toughness
value decreases with further increase in the
reinforcement percentage. Due to the phase
transformation and ability of the zirconia to
influence the microstructure of the matrix material,
by making them finer, brittleness is overcome.
VII. HARDNESS TEST RESULTS
Table 3 Brinnel Hardness for various wt.% of
reinforcenment
0
20
40
60
80
100
As
Cast
2% 4% 6% 8% 10%
Specimen Brinell Hardness
As Cast 70.2
2% 76.3
4% 80.4
6% 65.5
8% 68.8
10% 67.5

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Fig 12 Variation of Brinell Hardness for different
composition of ZrO2
From the above graph it can be seen that
the brinell hardness is increased with the increase
in percentage of reinforcement and reaches its
maximum value at 4%.And with further increase in
the reinforcement, the hardness tends to decrease.
At room temperature, the mechanical strength &
fracture toughness for Zirconia (ZrO
2
) is the most
powerful within all ceramic materials; therefore it
has another appellation “Ceramic Steel”. The
Vickers Hardness is about 1400HV.
VIII. MICROSTRUCTURE ANALYSIS
Fig 13 Microstructure of Al 6061 as cast ×300
Fig 14 Microstructure of 6% ZrO2 ×300
The homogenous distribution is achieved
by the shearing forced caused by stirring which
also averts settling of particles. Homogenous
distribution leads to better wear and mechanical
properties. The collection of particles in some
places is evident in cooling case, this is because of
porosity associated with it. Porosity is formed due
to entrapment of moisture and air.
IX. CONCLUSION
Aluminum metal matrix composite
materials are the most potential materials for future
automotive, aerospace and other sophisticated
applications. Al 6061 matrix composites reinforced
with Zirconium Oxide has been successfully
produced by the stir casting method.
1. The results from the work manifests that there
is increase in the fracture toughness in the
presence of zirconium oxide in the matrix
alloy. The composite with 6% ZrO2
reinforcement has shown highest value of
fracture toughness.
2. The result shows the increase in hardness for
4% weight fraction of zirconium oxide. The
hard reinforcement particles in the matrix will
obstruct the movement of dislocations ,as these
particles are harder than the matrix.
3. The yield strength and the ultimate strength of
the composite is reduced as the weight fraction
of ZrO2 is increased in the matrix.
4. Microstructure shows reasonable
homogeneous distribution of ZrO2 particles in
the composite.
REFERENCES
[1]. Anthony Kelly, Karl Zweben, “
Comprehensive composite materials:
design and application”, Elsevier, volume
6, ISBN-0-08-043724-9.
[2]. Shivaraja H. B & B. S. Praveen Kumar,
“Experimental Determination and
Analysis of Fracture Toughness of
MMC”, International Journal of Science
and Research (IJSR),2012.I.S.
[3]. K.B. Girisha, Dr. H.C.Chittappa,
“Preparation, Characterisation of Wear
Study of Al 356.1 Reinforced with
Zirconium Nano Particles “,
[4]. International Journal of Innovative
Research in Science, Engineering and
Technology, Vol. 2, Issue 8, August 2013
[5]. Jacobs and C.P. Bean, “Fine particles, thin
films and exchange anisotropy,” in
Magnetism, vol. III, G.T. Rado and H.
Suhl, Eds. New York: Academic, 1963,
pp. 271-350.
[6]. K. Elissa, “Title of paper if known,”
unpublished.
[7]. R. Nicole, “Title of paper with only first
word capitalized,” J. Name Stand.
Abbrev., in press.
[8]. Y. Yorozu, M. Hirano, K. Oka, and Y.
Tagawa, “Electron spectroscopy studies
on magneto-optical media and plastic
substrate interface,” IEEE Transl. J.
Magn. Japan, vol. 2, pp. 740-741, August
1987 [Digests 9th Annual Conf.
Magnetics Japan, p. 301, 1982].
[9]. M. Young, The Technical Writer’s
Handbook. Mill Valley, CA: University
Science, 1989.
[10]. P.O Babalola1, C.A Bolu1, A.O
Inegbenebor1 and K.M Odunfa,
[11]. “Development of Aluminium Matrix
Composites: A review” Online
International Journal of Engineering and
Technology Research, pp.1-11, Vol 2,
2014